1. Field
Example embodiments relate to a light sensing circuit, a method of manufacturing the same, and an optical touch panel including the light sensing circuit, and more particularly, to a light sensing circuit using an oxide semiconductor transistor, a method of manufacturing the light sensing circuit, and an optical touch panel including the light sensing circuit.
2. Description of the Related Art
Touch screens refer to apparatuses that allow input data to be directly input on a display screen in such a way that when, for example, a person's finger or a pen or something similar is brought into contact with a particular position on the display screen, the contact position is identified, and then a corresponding process is performed by software. To do this, touch screens further include a touch panel that is attached to a general display panel to perform the function described above. Examples of touch panels include resistive overlay touch panels, capacitive overlay touch panels, surface acoustic wave (SAW) touch panels, infrared touch panels, and piezoelectric touch panels. From among these, resistive overlay touch panels are the most popular. As technology advances, touch panels have been realized using various methods and as their prices have decreased, touch panels have become more commonly used. Recently, in-cell touch panels in which a touch sensor is integrated in a pixel of a display panel have been developed.
However, currently used touch panels operate only when a person's finger or a pen is brought into direct contact with the touch panels. Accordingly, when resistive overlay touch panels, which are the most widely used type of touch panel, are used, an upper or lower conductive layer may be damaged due to an external pressure. Moreover, although resistive overlay touch panels have an excellent sensing effect, they can be used only when a distance between the resistive overlay touch panels and a user is small. Thus, touch panels are used in a small or medium-sized display of, for example, a general desktop computer, a notebook computer, or a portable device, for example, a mobile phone or a navigation device. However, as display devices get larger, it may be difficult to use existing touch panels when a distance between a user and a display is large.
Recently, optical touch panels that may perform the same function as touch panels by sensing light have been introduced. In order to realize an optical touch panel, a light sensing circuit for sensing light is required. The light sensing circuit generally includes a light sensing element, and a switch circuit for outputting data from the light sensing element. For example, a photodiode basically having a PN junction of semiconductors, for example, silicon, is used as the light sensing element. However, since a photocurrent of a silicon photodiode is not large, the switch circuit requires a capacitor for accumulating charges for a predetermined period of time. Accordingly, the light sensing circuit increases in complexity and size and a parasitic capacitance is also increased, thereby making it difficult to manufacture large optical touch panels.